Various valve assemblies have heretofore been provided for draining a liquid which has accumulated in a closed vessel (e.g. fuel/water separator). Controlled drainage of the accumulated liquid, such as water, oftentimes presents a problem because of a vacuum environment which exists within the vessel interior. Such prior valve assemblies utilized for this purpose have been beset with one or more of the following shortcomings: (a) the assembly was of complex and costly construction; (b) the assembly required an inordinate amount of service and maintenance; (c) the assembly was bulky and awkward to manipulate; (d) the assembly was ineffective in providing controlled drainage of the accumulated liquid; and (e) the assembly was difficult to install on the vessel and replacement of the various components thereof was a costly and time-consuming operation.